Project Summary/Abstract Obesity poses a serious public health concern and has been identified as a risk factor for a variety of medical and psychosocial comorbidities. Thirty-five percent of college students have overweight/obesity and are in need of brief and simple weight loss interventions that complement their unstructured lifestyles. Implementation intentions, a widely-used strategy to pursue goals, facilitate goal-attainment for a wide variety of health-behaviors, including dietary change and weight loss, and may therefore be useful for dietary change and weight loss in college students; however, this has not been tested. A study is needed to evaluate an implementation intention intervention for dietary change and weight loss in this population. Additionally, little research has examined implementation intentions in naturalistic settings over time, which may weaken underlying mechanisms given strong environmental temptations and necessitate additional support. Fluency training of implementation intentions (i.e., training for speed and accuracy) and text message reminders over the course of an intervention should serve to improve encoding and retrieval, strengthening the underlying mechanisms of action of implementation intentions and thus enhancing intervention effects. Moreover, individuals with obesity have been shown to be low in working memory capacity (WMC), a moderator that may inhibit use of the skill. Therefore, fluency training and text message reminders meant to support encoding multiple intentions and monitoring multiple cues to prompt retrieval may be most beneficial for individuals low in WMC. Thus, this proposal aims to test the efficacy of an implementation intention intervention alone (IMP) and in combination with fluency training and text message reminders (IMP+) against a goal-intention control group (GOL) on self-regulatory weight loss behaviors. A three-group randomized-controlled intervention paradigm will be employed across four weeks. Ecological momentary assessment (EMA), which entails the repeated testing of participants in real time, will be used to provide an in-depth snapshot of implementation intentions use and their mechanistic role in behavior change during weeks 1 and 4 of the program. This will be the first study to examine implementation intention use with an externally-valid measurement tool. At post-treatment, weight and dietary change will be assessed. Students with overweight/obesity (n=75; ages 18-25) wanting to lose weight, but not currently enrolled in a weight loss program, will be assessed. This study is significant because it: 1) evaluates the use of a simple and effective transdisciplinary goal-striving strategy, alone and enhanced, for weight loss and diet change in college students with overweight/obesity, 2) considers cognitive moderators (i.e., WMC) that may interfere with intervention efficacy that are salient to individuals with obesity and identifies ways to attenuate their effect and, 3) provides the first examination of implementation intention usage in a naturalistic environment, to gain insight into the practical application of theoretical underlying mechanisms.